1. Field of the Invention
This invention is related to an improved method for determination of logPoct values for drug candidates.
2. Related Art
The importance of octanol-water partition coeffiecients (logPoct) is underscored, for example, by the generally observed correlation between a high lipophilicity (logPoct greater than 4.5) and a poor solubility.1 Computed values for drug molecules are often inaccurate, depending on the software used, by as much as two logPoct units, for any given compound or class of compounds. Data analyses and alerts such as the Lipinski""s xe2x80x9cRule-of-5xe2x80x9d2 would greatly benefit by the introduction of measured values, especially if they could be generated with high speed and accuracy. Thus, whenever possible, the computed values should be replaced by measured values, especially if the method requires only a very small amount of a new chemical entity, and can tolerate some impurities.
Lipophilicity of drug candidates is important since it is being used in the prediction of absorption, disposition and excretion.3 It is generally held that very lipophilic compounds are xe2x80x9cpreferredxe2x80x9d targets for metabolism, often leading to high clearance values and frequently correlates with a high plasma protein binding. A large volume of distribution, probably due to a high fraction of the compound bound to tissues, is often observed in the case of lipophilic compounds. Thus, a method that can accurately and rapidly yield logPoct values, is an important addition to the experimental tools available for physicochemical properties screening.
The classical shake-flask method, or variations of this method which have been described,4 are neither rugged not rapid enough for medium to high-throughput applications, and they are generally sensitive to impurities, and less amenable to automation than are reverse phase high performance liquid chromatography (RP-HPLC) methods.5 
(RP-HPLC) retention data have been shown to correlate well with absolute and relative lipophilicity values but, they have also been criticized as not being a true xe2x80x9creplacementxe2x80x9d for shake-flask values.4 Part of the criticism stems from the fact that many reports were limited in their scope, focusing either on fairly simple monofunctional solutes,6-7 or classes of analogs8 with a limited logPoct range. Furthermore, in several cases4, the slope of the logPoct vs. log kxe2x80x2 or log kxe2x80x2w, solvent was quite different from unity, casting doubts about the different balance of forces responsible for the two values. In these linear regression analyses, kxe2x80x2 represents the capacity factor of the solute at a given concentration of organic solvent, and kxe2x80x2w is the capacity factor extrapolated to 0% of the organic solvent. However we have found that, with a judicious choice of conditions, RP-HPLC methods might be defined, following Taylor9, as xe2x80x9cbeing in a class of their ownxe2x80x9d.
Another factor of great importance,5 is the reproducibility of the data from column to column, that is the reproducibility is likely to be dependent on packing chemistry and manufacturing of the columns. It might be argued that a pooling data from different columns will not be difficult, although xe2x80x9cscaling standardsxe2x80x9d might be needed. However, tests of reproducibility of the method from column to column should be performed, independently of the above arguments.
The speed of the determination and the ability to handle diverse structures and lipophilicity values are, of course, of paramount importance in an industrial research setting. These aspects translate into the capability of screening, with fairly modest resources, a fairly large number of compounds, with a good degree of accuracy applicable across a wide range of lipophilicity values.
There is a long felt need for a method for determining logPoct which would be accurate, rapid and possess a good dynamic range, together with being applicable to a variety of drug-like molecules.
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35. Waters Corporation, 34 Maple Street, Milford, Mass. 01757.
This invention provides a method of determining an experimental logPoct, herein designated ElogPoct for a chemical compound which comprises: introducing said chemical compound to the column of a reverse phase high performance liquid chromatograph; said column being an embedded amide functional group column; or a C-18 bonded column with low silanol activity35; and eluting said compound with a mobile phase containing MOPS buffer and a methanol/octanol mixture in which the proportions of said methanol/octanol mixture to said buffer are from 70 to 15% v/v; and with the proviso that said mobile phase does not contain an aliphatic amine; and detecting the retention time required to elute said sample from said column; and calculating ElogPoct from the retention time of said sample; and decrease the overall time.
In a preferred method, in order to optimize the time of single measurements, the compounds for which ElogPoct is to be determined are divided into groups according to calculated lipophilicity based on chemical structure34.
In a further preferred method, samples are divided into three log Poct ranges from xe2x88x920.5 to 1; 1 to 3; and greater than 3.
Column conditions and % methanol in MOPS buffer were determined as follows:
Preferably, the entire group of samples in a given range of calculated logPoct is run before the column is equilibrated to the next condition.
A further preferred method is calculating logPoct values based on chemical structures by a programmed computer and introducing samples in a defined logPoct range into said column by robotic means under the control of a programmed computer and calculating ElogPoct from the retention time of the sample by equation 3.